With the rapid development of mobile communication, application ways of multi-system with co-base station and shared antenna feeder are widely used at present, to share resources and reduce cost of the system device. Dual-frequency combiner is a necessary microwave device in shared antenna feeder system of 2G/3G. The combiner is used for combining and distributing the different systems, to save feed cables, simplify system and reduce cost. Additionally, the power supply of the device in the base station tower is realized by the radio frequency cable. The combiner connected in series with the feed cable should have the performance of transmitting direct current power.
Referring to the schematic diagram of FIG. 1, the combiner is a microwave device with three ports, including two direct current feed channels and two radio frequency signal channels. Each of the direct current teed channels includes a lumped parameter low-pass filter, a switch and a lightning protection device. The low-pass filter is used for suppressing high frequency radio frequency signal so that the control signals with pre-determined frequency (for example, 3 MHz) can pass therethrough. The switch is used for controlling the direct current power to pass or not. The radio frequency signal channel includes a band-pass titter and a blocking capacitor. Pass band range of the band-pass filter of two radio frequency signal channels is adapt to the frequency range of the two combined signals. The signal input from public port (Port 1) is distributed to Port 2 or Port 3. Contrarily, the signal input from Port 2 or Port 3 are combined and output from Port 1.
The frequency range of the radio signal in the 2G/3G antenna feeder system is 806 MHz-960 MHz and 17101 MHz-21700 MHz. Most of the current combiner products realize the performance of ultra wide band and direct current passing by microstrip circuit with dielectric substrate. The disadvantages of these products are large volume and small power capacity. Additionally, the passive intermodulation index is determined by characters or the dielectric substrate material and, therefore, it is difficult to control in mass production.